We will study the chemical and physical properties of the cell surface with particular emphasis on components necessary for growth control, cell recognition and cell differentiation. The techniques used will include protein fractionation, preparation of monoclonal antibodies, measurement of the distribution, mobility and rate of internalization of cell surface components by the use of fluorescent probes, and separation of different cell types by fluorescent sorter. The systems used will include 3T3 cells, Schwann cells from dorsal root ganglia, myoblasts and chick neural retina. We expect that these observations will serve to identify cell surface components required for all growth and differentiation and provide information regarding their function.